Detail of the head tube - this one is Megan's, I can tell from how the down tube is mitred. That "tab" will get hammered around the head tube once things are hot and tacked so we get a really solid attachment. note that there's room to add a reinforcing ring to the bottom of the head tube if we get really serious (it's more than 2mm thick tube anyway, but this is where the Filibus bikes often break)).